Field of the Invention
The present invention relates to a display device and a driving method thereof.
Discussion of the Related Art
An organic electroluminescent (EL) device used for an organic EL display is a spontaneous emission device having an emission layer formed between two electrodes. The organic EL device emits light in a manner in which electrons and holes are respectively injected into the emission layer from a cathode and an anode and combined to generate excitons. Light is emitted when an exciton drops from an excited state to a lower energy state.
In an organic EL display, when a scan signal, a data signal and power are supplied to sub-pixels arranged in a matrix, transistors included in selected sub-pixels are driven. Accordingly, the organic light-emitting diodes corresponding to the transistors emit light in response to an amount of current generated according to operations of the transistors, thereby displaying an image.
An organic EL display includes an organic light-emitting display device (hereinafter referred to as “RGBW OLED”) which has a sub-pixel structure including red, green, blue and white sub-pixels in order to prevent decrease of luminance of pure colors and color deterioration while increasing optical efficiency.
When each piece of RGBW data is 10 bits, 40 bits (10 bits×RGBW (four sub-pixels)) are needed per pixel.
In a conventional RGBW OLED, a process of converting an RGB data into an RGBW OLED data is typically desired. In addition, a process of storing an RGBW data in a frame memory is typically desired for image control purposes such as PLC (Peak Luminance Control).
The conventional RGBW OLED assigns a minimum amount of RGB data to W data and minimizes the quantity of RGB data. Accordingly, the frame memory does not need to store 40 bits per pixel since one piece of data from among the RGBW data can be converted to “0”.
The conventional RGBW OLED typically has 32 bits of data per pixel, which includes 2 bits (marking bits) for checking which data from among the input RGB data, which are not 40 bits, have been converted to “0”, data that are not “0” from among the input RGB data, and W data. That is, the conventional RGBW OLED stores, in the frame memory, a 32-bit data corresponding to 10 bits×3 sub-pixels+2 bits=32 bits, that is, 30 bits corresponding to 3 sub-pixels to which three pieces of data are respectively supplied and 2 bits corresponding to the marking bits indicating sub-pixels to which “0” is supplied.
As described above, the conventional RGBW OLED typically needs to convert one of RGBW data values to “0” in order to store a 32-bit data in the frame memory, and thus, the conventional RGBW OLED does not simultaneously emit light corresponding to the RGBW data. As a result, the conventional RGBW OLED may not implement its maximum luminance.